1. Field of the Invention
The present invention relates to a quantitative analytical method and apparatus for spectrometric analysis in which a sample is irradiated with radiation such as infrared light, and a concentration of a plurality of ingredients contained in the sample are measured on the basis of its absorptivities at a plurality of appointed wave number points across an absorption spectrum.
2. Description of Related Art
A Fourier transformation infrared spectrometer (hereinafter referred to as FTIR) 1 having a construction as shown in, for example, FIG. 11, has been used for quantitative analytical results. The FTIR 1 is composed of an analytical portion 2 and a data-treating portion 3 for processing an interferogram which is the output of the analytical portion 2.
The analytical portion 2 is further composed of a light source 4 constructed so as to emit parallel infrared beams, an interference mechanism 8 comprising a beam-splitter 5, a fixed mirror 6, and a movable mirror 7 movable in the X-Y direction, a cell 9 housing a sample to be measured therein and irradiated with the infrared beams from the light source 4 through the interference mechanism 8, and a detector 10 composed of a semiconductor detector and the like.
The data-treating portion 3 comprises a spectrum-operating portion 11 processing an absorption spectrum of data composed of, for example, a computer and a quantitative operating portion 12 capable of calculating concentrations of ingredients contained in the sample to be measured by applying Lambert-Beer's law to the calculated absorption spectrum.
In addition, the spectrum-operating portion 11 comprises an adding and averaging portion 13 for adding and averaging, for example, the data of the interferogram, a high-speed Fourier transforming portion 14, in which output data from the adding and averaging portion 13 are subjected to a high-speed Fourier transformation, and an operating portion 15 for carrying out a spectral operation to determine the ingredients to be measured on the basis of output data from the high-speed Fourier transforming portion 14.
In an FTIR 1 having the above-described construction, a reference sample and an unknown sample to be measured, are separately housed in the cell 9 in order to measure an interferogram of the reference sample and of the sample to be measured, respectively. These interferograms are subjected to a Fourier transformation to obtain a characteristic power spectra; that is, a spectra of beams which have been transmitted through the cell 9. A ratio of the power spectrum of the sample to be measured to the power spectrum of the reference sample is then determined. A value of this ratio is converted to an absorptivity scale to obtain the absorption spectrum of the sample.
In the quantitative operating portion 12, which is a latter stage of the data-treating portion 3, the concentrations of the ingredients contained in the sample to be measured can be calculated by applying Lambert-Beer's law to the calculated absorption spectrum. A display portion 16 can provide a visual indication of the concentrations of ingredients.
Problems have occurred in the prior art when the sample contains multiple ingredients which are to be simultaneously analyzed during a continuous measurement cycle. Additionally, when the amount of concentration of individual ingredients can vary widely, it is difficult to secure accurate readings. These problems frequently occur in the analysis of the by-products of combustion from vehicles.
Accordingly, a demand exists in the prior art to address these problems.